Ankle replacement system

ABSTRACT

A prosthesis suited for orthopedic implantation possesses a multi-piece stem component that supports an artificial joint surface that can articulate with another artificial joint surface in various ways. The prosthesis can be assembled in a snap fit and/or interlocking fashion that provides positive locking means without the use of screws or other fasteners. The prosthesis can accommodate fitment of a plastic joint surface made, e.g., from ultra high molecular weight polyethylene. The prosthesis is well suited for use in an ankle replacement system that can be installed using minimally invasive intramedullary guidance established with respect to the major axis of the tibia by minimally invasive access through the calcaneus, through an incision in the bottom of the foot. The prosthesis makes possible the installation of a total ankle system using minimally invasive anterior access to the ankle joint for making bony cuts and to install prosthesis components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application U.S. patent applicationSer. No. 11/374,760, filed on Mar. 14, 2006, which claims the benefitunder 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No.60/661,584, filed Mar. 14, 2005, and is entitled “Ankle ReplacementSystem.”

FIELD OF THE INVENTION

The invention relates to ankle replacement prostheses and systems, aswell as associated surgical instruments and procedures.

BACKGROUND OF THE INVENTION

Until the early to mid 1970's, patients with injured or diseased anklejoints commonly resulting from rheumatism, or degenerative or traumaticarthritis, had few options when their ankle joints failed. The mostcommon procedure to help these patients regain some use of their anklewas obliteration of the joint by fusion, a procedure that is stillcommonly used today. Fusion, however, rendered the ankle stiff andgenerally immobile relative to the lower leg, resulting in limited useand additional stresses on the knee and hip joints.

Probably the first reported use of total ankle prosthesis was byBuckholz in 1969. The medical community recognized that such anklereplacement led to largely increased use of the ankle joint because thereplacement permitted ankle ranges of motion which generally attemptedto mimic the natural human joint. Since that time, ankle replacementprostheses have become increasingly common in use and improved indesign.

There is, however, a need for a total ankle replacement system thatreduces the occurrence of subsidence and aseptic loosening whileretaining the majority of the foot's natural motion. There is also aneed for a less invasive surgical method to install such a device toprovide improved healing and a decreased failure rate.

SUMMARY OF THE INVENTION

The invention provides orthopedic prostheses and systems, as well asassociated surgical instruments and procedures.

One aspect of the invention provides a multi-piece stem component for aprosthesis. The multi-piece stem component is suitable for use in anysurgical procedure in which a stem is required for fixation of aprosthesis, whether it is a total joint implant, fusion (arthrodesis)implant, osteotomy fixation implant, or fracture fixation implant. Themulti-piece stem component configuration is ideally suited for securingbone components together in a minimally invasive procedure, in which asmall surgical opening is used to install large components. Two or moresmall stem components can be sequentially attached to one another insitu to make a larger stem assembly. Representative tools andmethodologies for installing a multi-piece stem component are alsoprovided.

Another aspect of the invention provides articulating artificial jointsurfaces comprising complementary ball-and-socket surfaces that not onlyarticulate, but also allow the artificial joint to rotate about an axis.This makes possible more uniform wear of the surfaces to maximizefunction and longevity of the prostheses.

Another aspect of the invention provides articulating artificial jointsurfaces comprising complementary ball-and-socket surfaces that not onlyarticulate and rotate about an axis, but also accommodate fore and aftand lateral translation of the mating joint surfaces relative to thenative bone.

Another aspect of the invention provides artificial articulating jointsurfaces, each of which comprises a saddle-shaped component. The saddleshape is geometrically characterized as a swept arc, comprising asurface defined by a first arc that is swept along a second arc that isperpendicular to the first arc. The geometry forms, for each surface, anelongated trough that curves along an axis.

Another aspect of the invention provides a prosthesis supporting anartificial joint surface that can be assembled in a snap fit and/orinterlocking fashion that provides positive locking means without theuse of screws or other fasteners.

Another aspect of the invention provides a prosthesis accommodatingfitment of a plastic joint surface made, e.g., from ultra high molecularweight polyethylene.

Another aspect of the invention provides an ankle replacement systemthat can be installed using minimally invasive intramedullary guidanceestablished with respect to the major axis of the tibia by minimallyinvasive access through the calcaneus, through an incision in the bottomof the foot. Intramedullary guidance along the axis of the tibia makesit possible to make properly oriented bony cuts of the talus and tibiathrough anterior access to the ankle joint. Proper overall alignment ofthe total ankle system is achieved in desired alignment and orientationwith all the natural axes of the native ankle joint it replaces, andimproved long term results are achieved.

Another aspect of the invention provides prostheses, tools, andmethodologies that make possible the installation of a total anklesystem using minimally invasive intramedullary guidance established withrespect to the major axis of the tibia. Desirably, minimally invasiveintramedullary guidance is established with respect to the major axis ofthe tibia using fluoroscopic visualization.

Another aspect of the invention provides prostheses, tools, andmethodologies that make possible the installation of a total anklesystem using minimally invasive anterior access to the ankle joint formaking bony cuts and to install prosthesis components.

Another aspect of the invention provides prostheses, tools, andmethodologies that make possible the establishment of an in-lineintramedullary path through the calcaneus, talus, and tibia.

Other objects, advantages, and embodiments of the invention are setforth in part in the description which follows, and in part, will beobvious from this description, or may be learned from the practice ofthe invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an anatomic view of a human lower leg and foot skeleton.

FIG. 2 is a perspective anatomic view of a total ankle replacementsystem in which a tibial artificial joint surface and a talar artificialjoint surface are mutually sized and configured for articulation torestore a range of motion that mimics the natural joint, the systemincluding a talar stem that supports the talar artificial joint surfaceand that bridges the talus to the calcaneous.

FIG. 3 is a perspective anatomic view of a total ankle replacementsystem in which a tibial. artificial joint surface and a talarartificial joint surface are mutually sized and configured forarticulation to restore a range of motion that mimics the natural joint,the system including a talar stem that supports the talar artificialjoint surface and that projects from posterior to anterior of the ankleinto the anterior head of the talus, without bridging the talus to thecalcaneous.

FIG. 4A is a perspective exploded view of a multi-piece tibial stemthat, when assembled, is sized and configured to support a tibialartificial joint surface of a type shown in either FIG. 2 or FIG. 3.

FIG. 4B is an assembled side view of the multi-piece tibial stem shownin FIG. 4A being installed in a tibia and supporting a tibial artificialjoint surface in association with a talar artificial joint surface.

FIG. 5 is an anatomic side view of a total ankle replacement systemcomprising articulating ball-and-socket artificial joint surfaces.

FIG. 6 is a side anatomic view of articulating artificial joint surfacesthat comprise complementary ball-and-socket surfaces that not onlyarticulate, but also allows the artificial joint to rotate about thetibial axis.

FIG. 7A is an exploded perspective view of articulating artificial jointsurfaces that comprise complementary ball-and-socket surfaces that notonly articulate and rotate about the tibial axis, but also accommodatefore and aft and lateral translation of the mating joint surfacesrelative to the tibia.

FIGS. 7B and 7C are side anatomic view of articulating artificial jointsurfaces shown in FIG. 7A when assembled and installed for use.

FIGS. 8A, 8B, and 8C are the articulating tibial and talar surfaces 22and 24 are perspective views of articulating artificial joint surfacesthat each comprise a saddle-shaped component, with arrows provided inFIGS. 8B and 8C showing the articulation of the surfaces duringup-and-down flexing of the foot (FIG. 8B) and side-to-side flexing ofthe foot (FIG. 8C).

FIG. 9 is a perspective view of the saddle-shaped talar artificial jointsurface secured in a snap-fit fashion to a talar stem having aconfiguration shown in FIG. 3.

FIG. 10 is an exploded perspective view of the saddle-shaped talarartificial joint surface and talar stem shown assembled in FIG. 9.

FIG. 11 is an anatomic view that illustrates a representative techniquefor drilling the anterior head of the talus from a posterior joint entryto install a talar stem of the type shown in FIG. 3 and FIG. 9.

FIG. 12A is a perspective exploded view of a total ankle replacementsystem that includes a tibial component that articulates with a talarcomponent having a talar artificial joint surface that can comprise aplastic material, e.g., ultra high molecular weight polyethylene, andthat can be assembled in an interlocking fashion on a talar stem.

FIG. 12B is a perspective assembled view of the total ankle replacementsystem shown in FIG. 12A.

FIG. 12C is a section view taken generally along line 12C in FIG. 12B.

FIG. 13 is a perspective exploded view of a tibial component having atibial artificial joint surface that can comprise a plastic material,e.g., ultra high molecular weight polyethylene, and that can beassembled in a sliding snap fit fashion on a tibial stem, which is shownto be a multi-piece stem of a type shown in FIG. 4A.

FIG. 14 is a perspective view of the underside of a platform that formsa part of the tibial component shown in FIG. 13, the platformaccommodating a sliding snap fit with the plastic tibial artificialjoint surface.

FIGS. 15A, 15B, and 15C are side sections views of the platform shown inFIG. 14 making a sliding snap fit with the plastic tibial artificialjoint surface.

FIGS. 15D, 15E, and 15F are perspective views of an installation toolbeing manipulated to make the sliding fit between the plastic tibialartificial joint surface and the platform as shown in FIGS. 15A, 15B,and 15C.

FIG. 16 is a side section view of the tibial component shown in FIG. 13,after assembly.

FIG. 17 is a perspective view of the tibial component shown in FIG. 13,after assembly, and in articulation with a talar component.

FIG. 18 is a perspective anatomic view of a native ankle joint, showingthe three natural X, Y, and Z axes of the joint.

FIG. 19 is a perspective view of an alignment tool, which serves thetask of aligning an ankle joint with the tibia during a procedure whichinstalls a total ankle replacement system of a type shown in previousfigures.

FIG. 20 is an exploded perspective view of a footholder assembly thatforms a part of the alignment tool shown in FIG. 19.

FIGS. 21A and 21B are assembled perspective views of the footholderassembly shown in FIG. 20, showing its ranges of horizontal and verticalmovement that make possible horizontal and vertical alignment of the legand ankle joint radiologically.

FIGS. 22A and 22B are, respectively, side and end views of thefootholder assembly shown in FIGS. 21A and 21B, showing the range ofvertical movement that makes possible vertical alignment of the leg andankle joint radiologically.

FIGS. 23A and 23B are, respectively, top and end views of the footholderassembly shown in FIGS. 21A and 21B, showing the range of horizontalmovement that makes possible horizontal alignment of the leg and anklejoint radiologically.

FIG. 24 is a side view of representative tools and methodologies, whichserve the task of establishing an in-line intramedullary path throughthe calcaneus, talus, and tibia.

FIG. 25A is a top view of representative tools and methodologies, whichserve the purpose of establishing anterior access to the ankle joint forthe purpose of making bony cuts in the talus and tibia to clear a jointspace for installation of the tibial and talar prosthesis platforms.

FIGS. 25B and 25C are side views of the representative tools andmethodologies shown in FIG. 25A in use to make bony cuts in the talusand tibia to clear a joint space for installation of the tibial andtalar prosthesis platforms.

FIG. 26 is a top perspective view of the tools and methodologies shownin FIG. 25A in use to make bony cuts in the talus and tibia to clear ajoint space for installation of the tibial and talar prosthesisplatforms.

FIGS. 27A and 27B are side views of representative tools andmethodologies, which serve the purpose of establishing an intramedullarypassage within the tibia, into which the stem component of the tibialplatform can be installed, making use of anterior access through thecleared joint space formed using the tools and methodologies of FIGS.25A, 25B, 25C, and 26.

FIGS. 28A to 28E show in perspective views representative tools andmethodologies, which serve the purpose of establishing atalar-calacaneal passage bridging the talus and calcaneus, in which thestem component of the talar platform 20 be installed making use of theanterior access through the cleared joint space formed using the toolsand methodologies of FIGS. 25A, 25B, 25C, and 26.

FIGS. 29A to 29D and FIG. 30 show in perspective views representativetools and methodologies, which serve the purpose of installing themulti-piece tibial stem (as also shown in FIGS. 4A and 4B) and platform,the stem being assembled in situ in the intramedullary passage formedwithin the tibia formed using the tools and methodologies shown in FIGS.27A and 27B.

FIG. 31 shows in a side view the installation of the calcaneal stemcomponent into the passage bridging the talus and calcaneus (see FIG.28E) formed using the tools and methodologies shown in FIGS. 28A to 28E.

FIG. 32 shows in a side view the placement of the talar artificial jointsurface on the calcaneal stem component installed using the tools andmethodologies shown in FIG. 31.

FIG. 33 shows in a side view the installation of the tibial artificialjoint surface on the platform installed using the tools andmethodologies shown in FIGS. 29A to 29D and FIG. 30.

FIG. 34 is a left side perspective view of a representative installationplatform to which a variety of jigs, fixtures, reamers, and auxiliaryplatforms of the form, fit, and function shown in FIGS. 19 to 33 may berigidly and simply affixed to the sequence of tasks, including (i) thealignment of the ankle joint with the tibia, (ii) the establishing of anin-line intramedullary path through the calcaneus, talus, and tibia;(iii) the establishing of anterior access for the purpose of makingproperly oriented bony cuts in the talus and tibia to install the tibialand talar platforms; and (iv) the installation of the tibial and talarplatforms.

FIG. 35 is a right side perspective view of the installation platformshown in FIG. 34.

DESCRIPTION OF PREFERRED EMBODIMENTS

This description is divided into logical sections for ease ofdisclosure. Section I introduces the reader to the anatomy of the lowerleg and ankle, to set the anatomic backdrop of the total anklereplacement systems and methods that will be described. Section IIprovides structural descriptions of representative embodiments of thetibial and talar-calcaneal components of total ankle replacement systemsand devices that have the desired form, fit, and function. Section IIIprovides descriptions of representative embodiments of systems, methods,and techniques useful for the implantation of total ankle replacementsystems and devices to achieve their desired form, fit, and function.

Although the disclosure hereof is detailed and exact to enable thoseskilled in the art to practice the invention, the physical embodimentsherein disclosed merely exemplify the invention, which may be embodiedin other specific structure. While the preferred embodiment has beendescribed, the details may be changed without departing from theinvention, which is defined by the claims.

I. Anatomy of the Lower Leg and Ankle

As FIG. 1 shows, the foot comprises fourteen phalanges or toe bones 11connected to the metatarsus bones 13. There are also seven tarsal bones14, of which the talus 15 supports the tibia 16 and the fibula 18, andthe heel bone or calcaneus 17. Of the tarsal bones, the talus 15 and thecalcaneus 17 are the largest and are adjacent to each other. The othertarsal bones include the navicular 19, three cuneiforms 21, and thecuboid 23.

II. Total Ankle Replacement System

A. Overview

FIG. 2 shows a total ankle replacement system 10. Generally speaking,the system 10 includes a tibial platform 12 that is sized and configuredfor installation on the tibia 16. As also shown in FIG. 2, the tibialplatform 12 desirably includes a tibial stem 28. The system alsoincludes a talar platform 20 that is sized and configured forinstallation on the talus 15. As also shown in FIG. 2, the talarplatform 20 includes a talar stem 26.

The tibial platform 12 carries a tibial artificial joint surface 22. Thetalar platform 20 carries a talar artificial joint surface 24. Thetibial artificial joint surface 22 and the talar artificial jointsurface 24 are bearing surfaces mutually sized and configured toarticulate. The articulating joint surfaces 22 and 24 replace thenatural ankle joint surfaces, which are removed (as will be describedlater), to restore a range of motion that mimics the natural joint.

The joint surfaces 22 and 24 may be made of various materials commonlyused in the prosthetic arts including, but not limited to, polyethylene,high molecular weight polyethylene (HMWPE), rubber, titanium, titaniumalloys, chrome cobalt, surgical steel, or any other total jointreplacement metal and/or ceramic, bony in-growth surface, sinteredglass, artificial bone, any uncemented metal or ceramic surface, or acombination thereof. The joint surfaces 22 and 24 may comprise differentmaterials. For example, the tibial joint surface 22 may comprise aplastic or other non-metallic material, and the talar joint surfacecomprise a metallic material. The reverse can be true, or the surfaces22 and 24 may each comprise the same type of materials (i.e.,metal-metal or plastic-plastic).

B. Representative Embodiments.

The tibial platform 12, the talar platform 20, and/or the articulatingartificial joint surfaces 22 and 24 they carry may be variouslyconfigured and posses various technical features. Representativeexamples of configurations and features will now be described.

1. The Stems

a. The Talar Stems

The talar stem 26 may be variously sized and configured. As shown inFIG. 2, the stem 26 bridges the talus to the calcaneous. This stem 26serves the dual function of supporting the talar platform as well asfusing the sub-talar joint, should that be necessary or beneficial tothe patient.

As shown in FIG. 2, the replacement system 10 incorporates manytechnical features disclosed in Reiley U.S. Pat. No. 6,663,669. Forexample, the talar platform 20 is fixed to the calcaneus 17 and/or thetalus 15, which can increase the amount of bone available for fixation.The fusion of the subtalar joint that the stem 26 provides allowsfixation of the talar platform 20 to both the talus 15 and calcaneus 17.Alternatively, the subtalar joint can be fused using any method commonto those of skill in the surgical arts including, but not limited to,fusion with poly(methylmethacrylate) bone cement, hydroxyapatite, aground bone and marrow composition, plates and screws, or a combinationthereof.

The enlarged available bone base provides prosthesis stability, andallows for anchoring of the talar platform 20 with, for example, screws.This design provides stability and stress absorption for the overallprosthetic ankle joint, and decreases the probability of prosthesisloosening and subsidence.

Still, prosthesis systems with talar stems 26 that do not bridge thetalus to calcaneous can also offer stability, reliable fixation, andlongevity. The talar stem 26 shown in FIG. 3 does not bridge the talusto the calcaneous. Instead, the stem 26 projects from posterior toanterior of the ankle into the anterior head of the talus. The talarhead is a large bony component of the talus, which offers a substantialbony structure to affix the talar platform 20. The subtalar joint can bestill be fused separately, if desired, using any methods just mentioned.

Any given talar stem 26 may be made of various materials commonly usedin the prosthetic arts including, but not limited to, titanium, titaniumalloys, tantalum, chrome cobalt, surgical steel, polyethylene,absorbable polymer, or any other total joint replacement metal and/orceramic, bony in-growth surface, sintered glass, artificial bone, anyuncemented metal or ceramic surface, or a combination thereof. The talarstem 26 may further be covered with various coatings such asantimicrobial, antithrombotic, and osteoinductive agents, or acombination thereof. These agents may further be carried in abiodegradable carrier material with which the pores of the surface ofthe talar stem 26 may be impregnated. See U.S. Pat. No. 5,947,893, whichis incorporated herein by reference. If desired, the talar stem 26 maybe coated and/or formed from a material allowing bony ingrowth, such asa porous mesh, hydroxyapetite, or other porous surface.

The talar stem 26 may be any size or shape deemed appropriate and isdesirably selected by the physician taking into account the morphologyand geometry of the site to be treated. The physician is desirably ableto select the desired size and/or shape based upon prior analysis of themorphology of the target bone(s) using, for example, plain film x-ray,fluoroscopic x-ray, or MRI or CT scanning. The size and/or shape isselected to optimize support and/or bonding of the stem 26 to thesurrounding bone(s). The stem 26 may be variable lengths from 2 cm to 12cm and variable widths from 4 to 14 mm. In a representative embodiment,a talo-calcaneal stem 26 is approximately 65 to 75 mm in length andapproximately 7 to 13 mm wide. While in the disclosed embodiment thestem has a circular cross-section, it should be understood that the stemcould formed in various other cross-sectional geometries, including, butnot limited to, elliptical, polygonal, irregular, or some combinationthereof. In addition, the stem could be arched to reduce and/or preventrotation, and could be of constant or varying cross-sectional widths.

The talar stem 26 may be with poly(methylmethacrylate) bone cement,hydroxyapatite, a ground bone composition, screws, or a combinationthereof, or any other fixation materials common to one of skill in theart of prosthetic surgery.

As will be described in greater detail later, the talar stem 26 mayadditionally have interlocking components, along its length or at itstop surface to assemble the stem 26 in situ and/or allow othercomponents of the talar platform 20 to lock and/or fit into the talarstem 26.

2. The Tibial Stem

Like the talar stem 26, the tibial stem 28 may be made of any totaljoint material or materials commonly used in the prosthetic arts,including, but not limited to, metals, ceramics, titanium,titanium-alloys, tantalum, chrome cobalt, surgical steel, polyethylene,absorbable polymer, or any other total joint replacement metal and/orceramic, bony in-growth surface, sintered glass, artificial bone, anyuncemented metal or ceramic surface, or a combination thereof. Thetibial stem 2 8 may further be covered with one or more coatings such asantimicrobial, antithrombotic, and osteoinductive agents, or acombination thereof. These agents may further be carried in abiodegradable carrier material with which the pores of tibial stem 28may be impregnated. See U.S. Pat. No. 5,947,893.

Also like the talar stem 26, the tibial stem 28 may be fixed into thetibia with poly(methylmethacrylate) bone cement, hydroxyapatite, aground bone composition, screws, or a combination thereof, or any otherfixation materials common to one of skill in the art of prostheticsurgery. In the illustrated embodiment, the tibial stem 28 is fixed tothe tibia 16 with screws. If screws are used, they can extendanteriorly, posteriorly, medially, laterally and/or at oblique angles,or any combination thereof.

The tibial stem 28 may be variable lengths from 20 mm to 300 mm andvariable widths from 6 mm to 20 mm. In the preferred embodiment, thetibial stem 28 is preferably at least 50 mm in length. Of course, itshould be understood that the disclosed tibial stem 28 could be ofvirtually any length, depending upon the size of the patient, his or herbone dimensions, and the anticipated future mobility of the patient. Ingeneral, a larger patient, having larger bones, with a high anticipatedmobility (i.e. he or she will be walking/running around quite a bit)would desirably have a longer stem 28 to provide increased stability andbroader distribution of stress to prevent subsidence, loosening, andtibial osteolysis. If desired, the stem 28 can incorporate ananti-rotational feature such as outwardly extending fins—for example,one or more fins, 0.5 to 25 cm long, 1 to 3 mm wide, sharp edges ordull, located along the stem 28—or a bow to the stem 28—for example,ranging from 1 to 10 degrees bow, anterior or posterior or lateral, orsome combination thereof. Moreover, if desired, the surface of thetibial stem 28 can incorporate irregularities such as wedges or points,desirably angled towards the knee, which inhibit and/or prevent thetibial stem 28 from subsiding. Alternatively, the width of the tibialstem 28 may vary along the length of the stem 28, further inhibitingand/or preventing rotation and/or subsidence.

As will be described in greater detail later, the tibial stem 28 mayadditionally have interlocking components along its length and/or at itslower surface to allow assembly the stem 28 in situ and/or allow othercomponents of the tibial platform 12 to lock into the tibial stem 28.

3. Multiple Piece Stem

FIG. 4A illustrates a multi-piece tibial stem 30 suitable for use in anysurgical procedure in which a stem is required for fixation of animplant, whether it is a total joint implant, fusion (arthrodesis)implant, osteotomy fixation implant, or fracture fixation implant. Inthe illustrated embodiment, the stem 30 comprises a top (i.e., superior)component 32, one or more mid components 34, and a bottom (i.e.,inferior) component 36. The top component 30 is desirably convex ordomed to facilitate advancement of the stem 30 in the direction of thetop component 32 within bone.

The multi-piece configuration is ideally suited for securing bonecomponents together in a minimally invasive procedure. Thisconfiguration is also ideally suited for minimally invasive surgeries inwhich a small surgical opening is used to install large components. Thisconfiguration allows a small surgical opening to be used to installlarge components at generally a right angle to or transverse thedirection of insertion of the individual stem components 32/34/36. Thisaspect of the multi-piece stem 30 will be very apparent after discussionof representative surgical procedure later.

Two or more small stem components 32/34/36 can be sequentially attachedto one another in situ (see FIG. 4B) to make a larger stem assembly. Forexample, a top component 32 may be joined with a bottom component 36.Alternatively, one or more mid components 34 may be placed between thetop and bottom components 32 and 36 to form a stem 30 of a desiredlength. The components 32/34/36 may be screwed together, as shown, orattached with a Morse taper, one-quarter turn, or other fixation means.Alternatively, the stem segments 32/34/36 can be fitted together with acombination of Morse tapers and threads, or with a combination of Morsetapers and external pins or screws.

As will be described in greater detail later, one or more of thecomponents 32/34/36 may include an internal hex 38 or other non-rotationconfiguration for engagement with a driver or other tool to facilitateadvancement of the component 32/34/36 within bone and/or to torque thecomponent 32/24/36 into the adjacent component 32/34/36, as shown inFIG. 4A. Similarly, one or more of the components 32/34/36 may alsoinclude an external hex 40 or other non-rotation configuration forengagement with a wrench or other tool to grasp or otherwise secure thecomponent 32/34/36 during installation.

As will be described in greater detail later, each component 32/34/36 isdesirably sized and configured to be individually installed through asmall incision, e.g., a small anterior opening in the ankle. In this way(see FIG. 4B), the individual components 32/34/36 can be sequentiallyjoined together in situ, e.g., within an intramedullary path in thetibia (which has been reamed-out in advance) and progressively advancedup the intramedullary path, top component 32 first. The last or bottomcomponent 36 is sized and configured to attach to a prosthesis (e.g.,the tibial platform 12) that would comprise the upper half of the ankleprosthesis.

The multi-piece configuration not only permits installation usingminimally-invasive procedures, but provides a means to install longfixation members or stems that might not be achievable if they wereconstructed of a single piece.

While the long or extended length of the multi-piece stem 30 isparticularly well-suited for use in the tibia, the multi-piece stem 30could be used in other long bones or in the talus as well.

4. The Articulating Artificial Joint Surfaces

The articulating artificial joint surfaces 22 and 24 may be made ofmaterials such as plastic (e.g., polyethylene), ceramic, or metal, orcombinations thereof (e.g., metal-backed plastic). They may possessvarious configurations and articulate in different ways. Variousrepresentative embodiments will now be described for purpose ofillustration.

a. Mating Concave/Convex Surfaces

As shown in FIG. 5, the basic geometry of the articulating surfaces 22and 24 can form a ball-and-socket joint. In this arrangement, thearticulating surfaces 22 and 24 comprise mating concave and convexsurfaces. In one arrangement, the tibial artificial joint surface 22comprises a concave dome, and the talar artificial joint surface 24comprises a convex dome that, when installed, mates with the concavedome. This mimics the configurations of the natural joint surfaces theyreplace.

As FIG. 5 shows, the convex dome of the talar surface 24 can comprise abutton-like structure that can be installed in a reamed-out pocketwithin the talus 15, without the use of a stem 26. The button-likestructure can be secured within the pocket without use of a stem 26 withpoly(methylmethacrylate) bone cement, hydroxyapatite, a ground bonecomposition, screws, or a combination thereof, or any other fixationmaterials common to one of skill in the art of prosthetic surgery. Tofacilitate placement, the button-like structure can include a peg 40 orsimilar appendage in lieu of a stem per se.

In this arrangement, the tibial surface 22 is secured to a stem 28 by aMorse taper connection that does not permit movement of the surface 22relative to the stem 2 8.

b. Rotating Concave/Convex Surfaces

FIG. 6 illustrates an embodiment in which the articulating surfaces 22and 24 comprise complementary ball-and-socket surfaces that not onlyarticulate, but also allows the artificial joint to rotate about thetibial axis. This makes possible more uniform wear of the surfaces 22and 24 to maximize function and longevity of the prostheses.

Similar to the embodiment previously described, the basic geometry ofthe articulating surfaces 22 and 24 comprises a ball-and-socket joint.The tibial artificial joint surface 22 comprises a concave dome, and thetalar artificial joint surface 24 comprises a convex dome that, wheninstalled, mates with the concave dome.

The talar artificial joint surface 24 is carried by a stem 26. Thesurface 22 is fixed to the stem 26 by a Morse-taper connection, so thatno relative movement can occur between this surface 22 and the talus.

The tibial artificial joint surface 22 is carried by a platform 12. Theplatform 12 is, in turn, coupled to a tibial stem 28 by a Morse taperconnection. No rotation between the platform 12 and the stem 28 canoccur. However, the connection between the platform 12 and the jointsurface 22 comprises a rotational fit. This fit is achieved between acylindrical collar 23 depending from the platform 46 that nests within amating trough 25 on the joint surface 22. This rotation fit allowsrotation of the surface 22 relative to the platform 12 about the axis ofthe stem 28 and thus about the axis of the tibia, to which the stem 28is fixed. This rotational coupling more freely accommodates rotation ofthe foot relative to the tibia, providing enhanced mechanicalequilibrium and stability.

c. Translating Surfaces

FIGS. 7A, 7B, and 7C illustrate an embodiment in which the articulatingsurfaces 22 and 24 comprise complementary ball-and-socket surfaces thatnot only articulate and rotate about the tibial axis, but alsoaccommodate fore and aft and lateral translation of the mating jointsurfaces relative to the tibia.

As in previous arrangements (see FIGS. 7A and 7B), the tibial artificialjoint surface 22 comprises a cup or socket-like surface, and the talarartificial joint surface 24 comprises a ball-like surface that, wheninstalled, mates with the cup-like surface of the tibial artificialjoint surface 22.

Also as in previous arrangements (still referring to FIGS. 7A and 7B),the talar artificial joint surface 24 is carried by a stem 26. Thesurface 22 is fixed to the stem 26 by a Morse-taper connection, so thatno relative movement can occur between this surface 22 and the talus.

The tibial artificial joint surface 22 is carried by a platform 12. Theplatform 12 is, in turn, coupled to a tibial stem 28 by a Morse taperconnection. No rotation between the platform 12 and the stem 28 canoccur. However, the connection between the platform 12 and the jointsurface 22 comprises a loose, non-interference fit between an oversizedhole 42 in the joint surface 22 and a lesser diameter tab 44 on theplatform 12. This loose coupling permits relative lateral (side-to-side)as well as anterior-to-posterior sliding or translation between theplatform 12 and the joint surface 22 (see FIG. 7C), as well asintermediate ranges of diagonal movement. The loose coupling also allowsrotation of the surface 22 relative to the platform 12 about the axis ofthe stem 28.

This loose coupling accommodates forward and sideways translation of thefoot relative to the tibia, as well as rotation of the foot relative tothe tibia. This feature makes possible uniform wear and uses all thesurface area to the fullest extent to maximize function and longevity ofthe prostheses. The translating ball and socket type articulationprovides mechanical equilibrium and stability. The articulatingspherical surfaces 22 and 24 maximize the contact area, therebyminimizing the contact pressure. This minimizes local surface stresses,in turn, minimizing wear on the joint and maximizing joint longevity.

The ball joint maximizes joint mobility. It accommodates the normalflexure of the ankle during walking or running. It also allows for thenormal side to side rotation of the normal ankle.

d. Saddle Surfaces

Previous embodiments show, as the basic articulating geometry, ball andsocket joints. In FIG. 8A, the articulating tibial and talar surfaces 22and 24 are shown to each comprise a saddle-shaped component. The saddleshape is geometrically characterized as a swept arc (which is ofconstant radius in a preferred embodiment), comprising a surface definedby a first arc (which is of constant radius in a preferred embodiment)that is swept along a second arc (which is also of constant radius in apreferred embodiment) that is perpendicular to the first arc. Thegeometry forms, for each surface 22 and 24, an elongated trough thatcurves along an axis.

As shown in FIG. 8A, the trough of the tibial saddle surface 22component nests within the trough of the talar saddle surface 24. Aninterface is thereby formed between the tibial and talar components ofthe prosthesis. The articulation occurs along this interface both alongthe curved axis of the trough, i.e. accommodating up and down flexing ofthe foot (see FIG. 8B), as well as transversely within the tough, i.e.,accommodating lateral (side to side) flexing of the foot (see FIG. 8C).

The saddle interface provides the joint with intrinsic stability, as thejoint wants to assume a position of stable static equilibrium. Somepatients will require a deep saddle trough because the surrounding softtissue supports for the ankle joint are compromised or weak. Otherpatients may require a less deep saddle trough because their joint hasmore supporting soft tissue. A more shallow saddle trough providesincreased ability for the joint to rotate about the tibial axis, whichis desirable.

As FIGS. 8A to 8C show, the saddle shaped tibial surface 22 can be sizedand configured to be fixed to a tibial stem 28 in any of the mannerspreviously described. In FIGS. 8A to 8C, the stem 28 can comprisecomprises a multi-piece stem 30 as earlier described and as shown inFIG. 4A. The talar component is desirably installed after the tibialcomponent has been inserted into the joint.

The talar component can be sized and configured in various ways. In theembodiment shown in FIGS. 9 and 10, the talar platform 20 is secured toa talar stem 26 having a configuration shown in FIG. 3, i.e., the stem26 does not bridge the sub-talar joint, but projects from posterior toanterior into the anterior head of the talus 15.

FIG. 11 illustrates a representative technique for drilling the anteriorhead of the talus 15 from a posterior joint entry to install the talarstem 26. A k-wire 52 is used to pierce from within the joint, in ananterior to posterior-lateral direction. The foot is then placed in thedorsi-flexion position, as shown. A conventional cannulated trocar (notshown) is placed over the k-wire 52 and advanced to pierce the joint ina posterior to anterior direction. A cannula 54 is passed over thetrocar, and the trocar is removed. The cannula 54 remains, establishinga percutaneous path to the talus 15. A cannulated drill 56 is placedover the k-wire 52 within the cannula 54. The anterior head of the talus15 is drilled to the proper depth to receive the stem 26. The stem 26 isinserted.

The talar platform 20 is secured to the stem 26 and nests on top of thetalus 15, which has been milled beforehand. As FIG. 10 best shows, theproximal end 76 of the stem 26 includes a male hex 78, or othernon-rotation configuration, that nests in a female hex 80 on the bottom74 of the talar platform 20. A cap screw 82, proceeding through thetalar platform 20 into the talar stem 26, affixes the stem 26 andplatform 20 together.

In the illustrated embodiment, the saddle shaped talar artificial jointsurface 24 snaps into the top of the talar platform 20 and rests in aload bearing nest defined by the platform 20. A pair of opposing tabs orprotrusions 68 from both sides of the talar artificial joint surface 24nest in slots 70 in raised pillars 72 on the talar platform 20, furtherensuring that the surface 24 is well secured to the talar platform 20.The snap-together interlocking configuration provides for easily removaland replacement of the talar artificial joint surface 24.

Before installing the surface 24, a sizing-piece, made of plastic orother suitable biocompatible material, can be slid into the joint spaceso the physician can determine the proper thickness of material toprovide the proper joint distention. When the proper size has beendetermined, the physician slides the actual talar artificial jointsurface 24 into the joint space and snap-fits it onto the platform 20.

This arrangement makes it possible to install and use a plastic jointsurface on the talar side of the prosthesis. For example, the talarartificial joint surface 24 can be formed of a durable biocompatibleplastic, e.g., Ultra High Molecular Weight Polyethylene (UHMWPE).Placement of a plastic component on the talar side rather than on thetibial side provides the maximum amount of plastic material availablefor strength and wear properties, while at the same time allowing forthe minimal amount of bone removal.

Another representative embodiment of a plastic talar-side component isshown in FIGS. 12A and 12B. The component shares many of the features ofthe component just described. In addition, the joint surface 24 rests onthe platform 20 upon a pair of spacing leg plates or spacers 58. Thespacers 58 are placed under the talar artificial joint surface 24 onopposing sides of the surface 24 (see FIG. 12C). The spacers 58 includeupwardly arched sides that nest within tabs 59 extending beneath thearched edges of the saddle-shaped joint surface 24. A locking plate 60fits on the platform 20 beneath the spacers 58 upon which the talarartificial joint surface 24 rests. Flanges 66 projecting from sides ofthe locking plate 60 lock into slots 61 on the talar platform 20.

The thickness and configuration of the spacers 58 and plate 60 can bevaried to accommodate individual patient needs and anatomy. In arepresentative embodiment, the spacers 58 and locking plate 60 are eachapproximately 1-2 mm thick.

The locking plate 60 is sized and configured with a memory to serve as aspring-lock. All the components of the talar assembly are frictionallylocked together, like a rubix cube, without the use of screws or othermechanical fasteners.

The frictionally interlocking design provides stability, as there are noinduced forces tending to drive the components from the joint space,because they are all interlocked. The anterior-posterior andmedial-lateral forces on the talar component may be substantial, but thetalar joint surface 24 is trapped-locked within the talar platform 20sidewalls and securely held in place.

The snap-together interlocking system just described provides a positivelocking means without the use of screws or other means. The interlockingdesign also provides the physician with a relatively simple means toreplace the talar artificial joint component 24 if it wears out. Toreplace the high-wear component 24, the physician makes a small anterioropening in the ankle to access the joint. The physician then removes thelocking plate 60 and spacers 58 and withdraws the worn component 24. Anew component 24 is inserted and locked into place.

5. Plastic, Snap Fit Tibial Component

A snap-fit assembly can also be incorporated into a tibial component. Asshown in FIG. 13, a tibial platform 12 includes a tibial stem 30, whichis shown to comprise a multi-piece stem as earlier described and asshown in FIG. 4A. In this embodiment, the tibial platform 12 and thestem 30 desirably comprise metal parts.

The tibial platform 12 carries a tibial artificial joint surface 22. Thejoint surface 22 is desirable made from a durable biocompatible plastic,e.g., Ultra High Molecular Weight Polyethylene (UHMWPE). Desirably, theplastic selected for the joint surface 22 is resiliently deformable,meaning that it will temporarily yield or bend in response to an appliedforce, but it will not permanently deform, but rather will return to itsnormal configuration when the force is removed. With this feature, thejoint surface 22 can be sized and configured to be snap-fitted to theplatform 12. It should be appreciated that alternative snap-fitassemblies could comprise a metal joint surface 22 and a resilientplatform 12, or resilient platform 22 and a resilient joint surface 12.

To secure the joint surface 22 to the platform 12, as FIG. 13 shows, theplatform 12 includes oppositely spaced, inwardly tapered side rails 90.The side rails 90 extend in an anterior to posterior direction along theunderside of platform 12. The tapered side rails 90 form a channel 92between them.

The topside of the artificial joint surface 22 (see FIG. 13) includes atab member 94. The tab member 94 is sized and configured to nest withinthe channel 92, by sliding the tab member 94 into the channel 92 in ananterior to posterior direction, as FIGS. 15A to 15C show.

As FIG. 14 shows, the underside of the platform 12 includes a shapeddepression or notch 96 near its anterior edge. Likewise, the topside ofthe artificial joint surface 22 includes an upwardly projecting lobe ordetent 98 near its anterior edge. The detent 98 is sized and configuredto rest within the notch 96.

More particularly, by applying force, the tab member 94 is made to enterand slide within the channel 92 (see FIG. 15A). The upwardly projectingdetent 98 will ultimately contact the anterior edge of the platform 12.As sliding force continues to be applied, the anterior edge of theresilient artificial joint surface 22 will yield by bending (see FIG.15B). The detent 98 will, as a result, ride under the anterior edge ofthe platform 12 and slide along the underbody of the platform 12, untilthe notch 96 is encountered (see FIG. 15C). When the notch 96 isencountered, the resilience of the joint surface 22 will snap-fit thedetent 98 into the notch 96.

As FIGS. 13 and 14 show, the underside of the platform 12 desirablyincludes a stop flange 190 along its posterior edge. The joint surface22 includes a mating proximal groove 192, which nests against the stopflange 190 to prevent over-travel of the joint surface 22 relative tothe platform when caused to slide in a posterior direction. Theengagement of the stop flange 190 and groove 92 is sized and configuredto occur in concert with the snap-fit engagement of the detent 98 withinthe notch 96.

As FIGS. 15D to 15F show, an installation tool 300 can be provided toaid in sliding the joint surface 22 into fitment with the platform 12.

In the illustrated embodiment, the installation tool 300 includes a body302 defining a channel 304 in which a manually operable plunger 306 iscarried for fore and aft sliding movement. With the plunger 306 pulledback into its most-aft position (see FIG. 15D), the joint surface 22 canbe loaded into the channel 304, detent 98-side first (the tab member 94slides within side rails that line the channel 304). The joint surface22 is placed into abutment with the plunger 306 within the channel 304.

As FIG. 15E shows, the platform 12 is coupled to the distal end of thebody 302 (e.g., with a mounting screw 312 carried on the distal end ofthe body 302 that engages a threaded receptacle 314 on the platform 12,along with an anti-rotational holding pin 308 on body 302 that fitswithin an aperture 310 on the platform 12). The body 302 holds thechannel 92 of the platform 12 in alignment to accept the tab member 94of the joint surface 22.

As FIG. 15F shows, forward advancement of the plunger 306 pushes thejoint surface 22, expelling it from the body channel 304 and into theplatform channel 92, until the notch 96 and detent 98 engage (as FIG.15C shows). Disengaging the screw 312 from the receptacle 314 andpulling back on the tool 300 disengages the holding pin 308 from theaperture 310, freeing the tool 300 from the now-assembled tibialcomponent.

When the tibial component is assembled (see FIG. 16), the tab member 94of the joint surface 22 is captured within the side rails 90 of theplatform 12; the detent 98 if the joint surface 22 is captured withinthe notch 96 of the platform; and the proximal groove 192 of the jointsurface 22 is captured within the stop flange 190 of the platform 12. Asa result, the joint surface 22 is held securely within the platform 12,which is, in turn, fixed in position by the stem 30. The joint surface22 is thereby positioned for stable articulation with a talar artificialjoint surface 24 (see FIG. 17), which is, in turn, fixed in position bya stem 26.

III. Implantation

A. Intramedullary Guidance

Desirably, the ankle replacement system 10 is installed using minimallyinvasive intramedullary guidance. Intramedullary guidance is establishedwith respect to the major axis of the tibia by minimally invasive accessthrough the calcaneus, through an incision in the bottom of the foot.Intramedullary guidance along the axis of the tibia makes it possible tomake properly oriented bony cuts of the talus 15 and tibia 16 throughanterior access to the ankle joint. Proper overall alignment of thetotal ankle system 10 and. improved long term results are achieved.

Using installation tools, systems, and methods that incorporateintramedullary guidance, the total ankle system 10 can be installed indesired alignment and orientation with all the natural axes of thenative ankle joint it replaces. FIG. 18 shows these natural axes toinclude the anterior to posterior axis (Y-horizontal axis) of rotationof the ankle joint, the natural medial-to-lateral axis (X-horizontalaxis) of rotation of the ankle joint, and the naturalsuperior-to-inferior axis (Z-vertical axis) of alignment of the anklejoint with the major axis of the tibia. By establishing and maintainingproper alignment of the anterior to posterior axis (Y-horizontal axis)of rotation, the ankle replacement system 10 establishes and maintainsthe desired degree of plantar-dorsi (“up and down”) flexion of the foot.By establishing and maintaining proper alignment of the naturalmedial-to-lateral axis (X-horizontal axis) of rotation, the system 10establishes and maintains the desired degree of inversion/eversion (“inand out”) rotation of the foot. By establishing and maintaining properalignment of the natural superior-to-inferior axis (Z-vertical axis) ofalignment of the ankle joint with the long axis of the tibia, the system10 is accurately oriented with respect to the central tibial axis of theleg, so that intramedullary support can be achieved by in line drillingof the calcaneous 17 and talus 15 in a single drilling step usingfluoroscopic guidance.

B. Installation Tools, Systems, and Methods

Representative installation tools, systems, and methods will bedescribed that are ideally suited for use in ankle replacementprocedures (i.e., the installation of a prosthetic replacement foreither or both of the tibial and talar ankle joint surfaces), as well asprocedures involving fusions in an ankle replacement procedure (e.g.,subtalar fusions, pan-talar fusions, or triple arthrodeses).

The representative installation tools, systems, methods accomplish thetasks of (i) the alignment of the ankle joint with the tibia, (ii) theestablishing of an in-line intramedullary path through the calcaneus,talus, and tibia; (iii) the establishing of anterior access for thepurpose of making properly oriented bony cuts in the talus and tibia toinstall the tibial and talar platforms 12 and 20; (iv) the installationof the tibial and talar platforms 12 and 20.

Representative embodiments of each of these tasks and related tools,systems, and methods will now be described.

1. Alignment of the Ankle Joint with the Tibia

FIG. 19 shows a representative alignment tool 100, which serves the taskof the alignment of the ankle joint with the tibia during a prosthesisinstallation procedure. The alignment tool 100 includes a footholderassembly 102 and a leg rest 104. The footholder assembly 102 includes afoot rest 106, to which the foot is secured by a foot clamp 106 and heelclamps 108 during an prosthesis installation procedure. The calf of theleg is suitably secured to the leg rest 104. Together, the footholderassembly 102 and the leg rest 104 hold the foot and ankle relative tothe leg during an installation procedure.

As FIG. 19 shows, the footholder assembly 102 is sized and configuredfor pivoting, under control of the physician, from a vertical or uprightcondition (shown in solid lines in FIG. 19) toward a more horizontal ortilted condition (shown in phantom lines in FIG. 19). In the uprightcondition, the assembly 102 serves to hold the ankle joint in a desiredorientation with respect to the natural anterial-to-posterior andmedial-to-lateral axes. By establishing and maintaining proper alignmentof both the anterior/posterior and medial/lateral axes, the anklereplacement system 10 establishes and maintains proper stressdistributions through the walking gait. The assembly 102 can be pivotedin a controlled fashion to cause flexion of the ankle joint, if and whendesired during the installation procedure. The footholder assembly 102can be locked by the physician in any desired orientation between thefull upright condition and full pivoted condition.

The footholder assembly 102 also allows the ankle joint to be preciselyoriented and maintained, using fluoroscopy, in a desired alignment withthe major axis of the tibia. As FIG. 20 shows, the footholder assembly102 includes, in addition to the foot rest 106, a back plate 112 andmid-plate 114, which is sandwiched between the foot rest 106 and theback plate 112.

The mid-plate 114 is coupled to the foot rest 106 by sliding dovetailcouplings 116 for up-and-down (vertical) movement relative to the footrest 106. A pair of oppositely spaced alignment rods 118 is carried bythe mid-plate 114. The alignment rods 118 lay in the same horizontalplane. The alignment rods 118 extend from the mid-plate throughvertically elongated slots 120 in the foot rest 106, so that, in use(see FIG. 19) the rods 118 lay on opposite sides of the tibia in themedial-to-lateral plane. Vertical movement of the mid-plate 114 movesthe alignment rods 118 up-and-down in unison within the slots 120 onopposite sides of the foot rest 106 (see FIG. 21B).

The back plate 112 is coupled to the mid-plate 114 by sliding dovetailcouplings 122 for side-to-side (horizontal) movement relative to thefoot rest 106. A pair of oppositely spaced alignment rods 124 is carriedby the back plate 112. The alignment rods 124 lay in the same verticalplane. The alignment rods 124 extend from the back plate 112 above andbelow the foot rest 10 6, so that, in use (see FIG. 19) the rods 124 layon opposite sides of the tibia in the anterior-to-posterior plane.Horizontal movement of the back plate 112 moves the alignment rods 124side-to-side in unison above and below the foot rest 106 (see FIG. 21A).

The back plate 112 also carries a bushing 126. The bushing 12 6 extendsthrough openings 128 in the mid-plate 114 and foot rest 106 andterminates at or near the plane of the foot rest 106 against which thebottom of the foot contacts. The center of the bushing 126 coincideswith the intersection of the horizontal plane of the rods 118 and thevertical plane of the rods 124.

The rods 118 and 124 are made of materials that are visualized byfluoroscopy.

In use, the leg and foot are prepped for surgery. The physiciandesirably makes an anterior incision to gain initial access to the anklejoint. The foot and lower leg are placed in the foot rest 106 and legrest 104. The physician estimates the ankle's axis of dorsi-plantarrotation and visually aligns the ankle to the axis of rotation of thealignment tool 100. The foot rest 106 is adjusted to rotate the foot sothat the big toe is pointing essentially vertically. The forefoot andheel are secured to the foot rest 106 with the clamps 108 and 110already described. The leg rest 104 is adjusted to the calf so that thetibia 16 is approximately parallel to the floor. The foot and calf aredesirably aligned so that the anterior-posterior (A-P) line of thetalus's trochlea is essentially vertical.

As shown in FIGS. 17A and 17B, a fluoroscopy unit 130 is aligned to themedial-lateral rods 118. When aligned, the rods 118 appear as one influoroscopy. The physician moves the mid-plate 114 to align the rods 118to the center axis (Z-axis) of the tibia 16. Suitable manual or poweredalignment controls (not shown) can be provided for this purpose. Whenthe desired medial-to-lateral alignment of the rods 118 with the z-axisis accomplished, the mid-plate 112 is locked to the foot rest 106.

As FIGS. 18A and 18B show, the fluoroscopic unit 13 0 is moved ninetydegrees to an anterior to posterior position. The fluoroscopy unit 130is aligned to the anterior-to-posterior rods 124. When aligned, the rods124 appear as one in fluoroscopy. The physician moves the back plate 112to align the rods 124 to the center axis (Z-axis) of the tibia 16.Suitable manual or powered alignment controls (not shown) can beprovided for this purpose. When the desired medial-to-lateral alignmentof the rods 124 with the z-axis is accomplished, the back plate 112 islocked to the foot rest 106.

The pairs of rods 118 and 122 (respectively horizontal and vertical) areused in concert to minimize parallax with the fluoroscopy procedure.When the rods 118 and 122 both optically “blend” into one, signifyingalignment, true horizontal or vertical alignment of the leg and anklejoint is achieved radiologically. For each pair of rods, one rod can befashioned to be fluoroscopically distinguished from the other, e.g., onerod can be grooved, while the other is smooth.

Once centering is complete, all guide rods 118 and 124 can be removed toallow unobstructed surgical access to the ankle joint.

2. Establishing an in-Line Intramedullary Path Through the Calcaneus,Talus, and Tibia

FIG. 24 shows representative tools 132. and methodologies, which servethe task of establishing an in-line intramedullary path through thecalcaneus, talus, and tibia. The tools 132 include a bottom foot cannula134 which establishes an intramedullary guide path through the calcaneusand talus that leads into the tibia.

The bushing 126 on the back plate 112 is slaved to alignment with theaxis of the tibia by alignment of the rods 118 and 124 to the sameanatomic target. Thus, after using the alignment tool 100 as justdescribed to align the ankle joint with the tibia, in line drilling ofthe center of the ankle and tibia for introduction of the bottom footcannula 134 is made possible, because the bushing 126 has been aligned,by alignment of the rods 118 and 124, to achieve the desiredline-drilling position up through the bottom of the foot.

There are various minimally invasive surgical techniques for introducingthe bottom foot cannula 134. In one representative embodiment, thebushing 126 is temporarily separated from the back plate 112 (e.g., byunscrewing) to provide access to the bottom of the foot. The physicianuses a scalpel to make an initial incision in the bottom of the foot,and the bushing 126 is replaced. A cannulated trocar loaded with ak-wire (not shown) can be inserted through the bushing 126, into thebottom of the foot, until the calcaneous 17 is contacted and the k-wireis firmly set into the calcaneous 17. The trocar can then be removed,and the k-wire lightly tapped further into the calcaneous 17. In arepresentative embodiment, the bushing 126 measures 6 mm in diameter,and the cannulated trocar can be 6 mm loaded with a 2.4 mm k-wire. Thephysician can now operate a cannulated first reamer (e.g., 6 mm) (notshown) over the k-wire up into the calcaneous 17 and talus 15approximately 30 mm. The first reamer opens an access path for insertionof the bottom foot cannula 134.

Withdrawing the first reamer and bushing 126, the physician can nowinsert the bottom foot cannula 134 (as shown in FIG. 24). With thebottom foot cannula 134 in place, a second reamer 136 (e.g., 5 mm) canbe operated through the cannula 13 4 to drill approximately another 100mm through the talus 15 and up into the tibia 16. Fluoroscopy may beused, if desired, to verify the accuracy of the drilled hole.

An intramedullary guide path has been established through the calcaneusand talus leading into the tibia. The presence of the bottom footcannula 134 maintains the guide path in alignment with the axis of thetibia.

3. Establishing Anterior Access and Making Bony Cuts in the Talus andTibia

FIGS. 25A, 25B, 25C and FIG. 26 show representative tools 138 andmethodologies, which serve the purpose of establishing anterior accessto the ankle joint for the purpose of making bony cuts in the talus andtibia to install the tibial and talar platforms 12 and 20.

In the representative embodiment, the tools 138 include a cutting guidefixture 140 which is installed and stabilized over the ankle joint in ananterior position to the ankle joint. The cutting guide fixture 140 issecured to an underlying frame 142 to which the alignment tool 100 isalso attached.

As FIG. 25A shows, the cutting guide fixture 140 includes a superiorbone cutting blade guide 144 and an inferior bone cutting blade guide146.

The cutting guide fixture 140 also includes apertures for receivingfixation pins 148 adjacent the blade guides 144 and 146. In arepresentative embodiment, the pins 148 can comprise 2.4 mm Steinmannpins. A pair of the pins 148 are drilled adjacent the superior bladeguide 144 into the tibia 16, and the other pair of the pins 148 aredrilled into the talus 15 adjacent the inferior blade guide 146. Tomaximize operating field space, the pins 148 may be cut flush at thefixture 140, if desired. The operating field of the ankle joint isthereby stabilized, as shown in FIG. 25A.

As FIG. 25A also shows, the cutting guide fixture 140 also includes anaperture 150 for establishing an anti-rotational notch. The physiciancan form the anti-rotational notch, e.g., by using a drill and lockcollar (e.g. 4 mm) operated through the aperture. As FIG. 25A shows,using fluoroscopy, the bottom foot cannula 134 is kept in the foot, butout of the way of superior blade guide 144 and the intended location ofthe anti-rotation notch 150.

When establishing the anti-rotational notch, the physician desirablynotes from the drill the approximate depth of the underlying bone. Onthe superior and inferior saw blades 152 and 154 (see FIGS. 20B and20C), the physician notes the depth required based upon the previouslymeasured drill depth.

As FIG. 25B shows, the superior saw blade 152 is operated through thesuperior blade guide 144 to cut the top surface of the tibia 16.

Retaining the bottom foot cannula 134 within the foot while making bonycuts results an enhanced level of accuracy, because there is essentiallyno relative movement of the joint components during the drilling andsawing operations. Considerable force is often exerted upon the jointduring drilling and sawing operations, which can move the joint out ofthe desired orientation for optimal prosthesis placement. The bottomfoot cannula 134 helps ensure the joint components maintain the correctalignment relative to one another so that the resulting cuts are moreaccurately positioned.

Using fluoroscopy, the bottom foot cannula 13 4 is then retracted out ofthe way of inferior blade guide 146 (see FIG. 25C). As FIGS. 20C and 21show, the inferior saw blade 154 is operated through the inferior bladeguide 146. The bottom surface of the talus 15 is cut to the depthpreviously noted.

The bottom foot cannula 134 is reinserted into the foot and both sidesof the joint space are cut using side saw blade guide slots 156 (seeFIG. 25A).

The fixture 140 and pins 148 can now be removed. With a roundedosteotome, the corner of the joint space is cut out. The sides of theanti-rotation notch are cleaned so that the sides are essentiallyvertical. Loose bone pieces are removed and the cleared joint spaceirrigated. FIG. 27A shows the cleared joint space 158 and the anterioraccess it provides for the insertion of other installation tools and thecomponents of the tibial and talar platforms 12 and 20.

4. Creating Passages for Stem Components

In the illustrated embodiment, both tibial and talar platforms 12 and 20include respective stem components. As previously described, these stemcomponents provide enhanced fixation and support to the platforms. Thecreation of the passages for installation of these stem components inthe tibia and talus will now be described.

a. Boring the Tibia for the Tibial Stem

FIGS. 27A and 27B show representative tools 160 and methodologies, whichserve the purpose of establishing an intramedullary passage within thetibia, into which the stem component of the tibial platform 12 can beinstalled, making use of anterior access through the cleared joint space158.

In the representative embodiment, the tools 160 include a tibial stemdriver 162 having a threaded end and a tibial stem reamer 164, which canbe removably screwed onto the threaded end of the driver 162. Theinstallation of the bottom foot cannula 134 (previously described) makesits possible to couple of the reamer 164 to the driver 162 using theanterior access that the cleared joint space 158 provides. As shown inFIG. 27A, the threaded end of a tibial stem driver 162 can be insertedthrough the bottom foot cannula 134 to the cleared joint space 158. AsFIG. 27A shows, the physician has open anterior access here to insertthe tibial stem reamer 164 into the cleared joint space 158 and to screwthe reamer 164 onto the driver 162.

The reamer 164 desirably includes a bullet-shaped nose that fits withinthe previously formed 5 mm passage in the tibia 16. Entering thepassage, the reamer 164 enlarges the intramedullary tibial passage, asFIG. 27B shows. A depth mark can be noted on the driver 162 so that thetibia 16 is reamed for another approximately 70 mm, as FIG. 27B shows.

The physician can retract the driver 162 and the reamer 164 throughbottom foot cannula 134 to expose the reamer 164 with the joint space158. There, the physician can unscrew the reamer 164 from the driver 162to withdraw the reamer 164 through the anterior access. The driver 162can be withdrawn from the bottom foot cannula 134.

The intramedullary passage for installation of the tibial stem hasthereby been established.

b. Boring of the Talus and Calcaneus for the Calcaneal Stem

FIGS. 28A to 28D show representative tools 166 and methodologies, whichserve the purpose of establishing a talar-calacaneal passage bridgingthe talus and calcaneus. The stem component of the talar platform 20 canbe installed in the talar-calacaneal passage. The tools 166 andmethodologies operate by anterior access through the previously-clearedjoint space 158.

In the representative embodiment, the tools 166 include a calcanealdrill pin fixture 168 (FIG. 28A) and a companion calcaneal orientationfixture 170 (FIG. 28B). The drill pin fixture 168 establishes theanterior-to-posterior drill angle for formation of the talar-calcanealpassage, into which the calcaneal stem is eventually installed. Theorientation fixture 170 couples to the drill pin fixture 168 to aid inestablishing a desired medial-to-lateral orientation of the drill path.

Prior to use of the drill pin fixture 168 (see FIG. 28A), the footholderassembly 102 is pivoted out of its upright condition to rotate the footto maximum plantar flexion. As FIG. 28A shows, the drill pin fixture 168is installed into the flexed open joint space 158. An orienting pin 172is slid up the bottom foot cannula 134 and joined to an aperture in thepin fixture 168. With the orientation pin in place, the bottom footcannula 134 can be withdrawn.

The orientation fixture 170 is coupled to the pin fixture 168 (as FIG.28B shows). In the illustrated embodiment, the drill pin fixture 168includes an appendage 174 over which the orientation fixture 170removably fits. The orientation fixture 170 includes a symmetrical arrayof medial-lateral side arms 176, which sweep in a curved path into aspaced apart facing relationship at their terminal ends. Grasping thearms 176, the fixture 170 can be manipulated side-to-side orrotationally. Such movement of the orientation fixture impartscomparable movement to the pin fixture 168, thereby changing themedial-to-lateral orientation of the pin fixture 168 with respect to thecalcaneus. The orientation fixture 170 is manipulated to place theterminal ends of the arms 176 in an equally spaced orientation on eitherside of the calcaneous 17.

As shown in FIG. 23C, once the pin fixture 168 has been oriented, a pairof fixing pins 178 are inserted into side holes pin fixture 168, tosecure the pin fixture to the talus 15.

As FIG. 28C also shows, the physician drills a guide pin 180 into thecenter hole of the pin fixture 168, approximately 65 mm into thecalcaneus 17. In a representative embodiment, the pin 160 comprises a2.4 mm Steinmann pin. The fixing pins 178 and the pin fixture 168 cannow be removed, leaving the guide pin 180 in the calcaneous 17.

As FIG. 28D shows, a calcaneal reamer 182 is inserted over the guide pin18 0 and advanced approximately 65 mm into the calcaneous 17. Thecalcaneal reamer 182 is withdrawn, leaving the formed passage P (seeFIG. 28E) into which the calcaneal stem will eventually be inserted.

The footholder assembly 102 is pivoted back to its original uprightposition. The bottom foot cannula 134 is reinserted.

In this representative way, the trans-talar-calcaneal passage forinstallation of the calcaneal stem can be established.

5. Installing the Tibial Stem and Platform

FIGS. 29A to 29D and FIG. 30 show representative tools 184 andmethodologies, which serve the purpose of installing the tibial stem 30and platform 12.

In the illustrated embodiment, the tibial platform 12 is secured withinthe tibia 16 by a multi-piece stem 30 of the type previously described,as is shown in FIGS. 4A and 4B. In an earlier described installationsequence, and as shown in FIGS. 27A and 27B, an intramedullary passagehas been previously formed within the tibia to receive the multi-piecestem component 30.

In this installation sequence, as in previously described sequences ofthe installation, installation of the multi-piece stem component 30takes advantage of the anterior access provided to the cleared jointspace 158, as well as the calcaneal access provided by the bottom footcannula 134.

As FIG. 29A shows, the physician inserts the top tibial stem component32 into the joint space 158 through the previously formed anterioraccess. The tools 184 include a wrench 200 or other suitable tool. Thewrench 200 engages the exterior stem flats of the top stem component 32,gripping the top stem component 32. The top stem component 32 isadvanced partially up into the preformed tibial passage. The wrench 200abuts against the cut tibial bony surface, checking the advancement ofthe top stem component 32 beyond the superior confines of the clearedjoint space 158.

As shown in FIG. 2 9B, a mid stem component 34A, is inserted through theanterior incision. The tools 184 includes an intramedullary driver 186that is advanced through the bottom foot cannula 134 into the clearedjoint space 158. The driver 186 includes a male hex fitting 188 at itsdistal end. The hex fitting 188 of the driver 186 mates with theinternal female hex 3 8 inside the mid stem component 34A (the internalfemale hex 38 is shown in FIG. 4A). With the wrench 200 engaging the topstem component 3 2 to keep it from rotating, the physician twists thedriver 186 to torque the threaded male end of the mid stem component 34Ainto the threaded female end of the top stem component 32. This joinsthe top and mid stem components 32 and 34A. Once tightened, the wrench200 is switched from the top stem component 32 to the stem flats of themid stem component 34A. The physician axially advances the driver 186 topush the top stem component 32 beyond the confines of the cleared jointspace 158 and up into the tibial passage.

As FIG. 29C shows, the hex fitting 188 is withdrawn from the mid stempiece 34A, and the driver 186 is withdrawn sufficient to permit theinsertion of a second mid stem component 34B through the anterior accessinto the joint space 158. The sequence just described is repeated. Thehex fitting 188 of the driver 186 mates with the internal female hex 38inside the second mid stem component 34B. With the wrench 2 00 engagingthe first mid stem component 34A to keep it from rotating, the physiciantwists the driver 186 to torque the threaded male end of the second midstem component 34B into the threaded female end of the first mid stemcomponent 34A. Once tightened, the wrench 200 is switched to the stemflats of the second mid stem component 34B. The physician axiallyadvances the driver 186 to push the first mid stem component 34A,proceeded by the top stem component 32, beyond the confines of thecleared joint space 158 and up into the tibial passage.

Additional mid stem components can be installed in this fashion,depending upon the intended final length of the stem 30.

In turn, when insertion of a bottom stem component 36 is desired (thiscomponent is shown in FIG. 4A), the hex fitting 188 is withdrawn fromthe then end-most assembled stem piece. The driver 186 is withdrawnsufficient to permit the insertion of the bottom stem component 36 intothe anterior incision. As FIG. 29D shows, the hex fitting 188 of thedriver 186 engages the internal female hex 38 inside the bottom stemcomponent 36. With the wrench 200 engaging the end-most assembled stemcomponent (shown for purpose of illustration to be the second mid stemcomponent 34B), the physician twists the driver 186 to torque thethreaded male end of the bottom stem component 36 into the threadedfemale end of the first mid stem component 34A. The wrench 200 isswitched to the flats of the bottom stem component 36. Using the driver186, the physician axially advances the assembled multi-piece stem 30into the tibial passage, beyond the confines of the cleared joint space158.

In an alternative arrangement, the bottom stem component 3 6 need nothave an internal hex, in which case the bottom stem component 36 may betorqued onto the then end-most assembled stem piece using a threadeddriver or other suitable tool inserted into the joint space 158.

As FIG. 3 0 shows, holding the bottom stem component 36 with the wrench200, the physician inserts a tibial platform 12 into the joint space.The physician uses the driver 186, advanced through the bottom footcannula 134 to couple the tibial platform 12 to the bottom stemcomponent 36, e.g., by inserting a male Morse fitting on the platform 12into a corresponding female fitting on the bottom stem component 36.

If desired, the platform 12 may be marked for easy placement reference.For example, the face may be marked ANT-R (for the right foot or ANT-L,for the left foot) to clearly indicate that the face is placed facinganterior (not shown).

If desirable, bone cement may be applied to the top of the tibialplatform 12. The platform 12 is then firmly pushed against the bottom ofthe tibia 16 to push the stem 3 0 firmly into the tibia 16 and theanti-rotation notch 150.

6. Assembly and Installation of the Talar/Calcaneal Stem and TalarArtificial Joint Surface

As previously described, FIGS. 28A to 28E show representative tools 166and methodologies, which serve the purpose of establishing a passage Pbridging the talus and calcaneus (see FIG. 28E), into which the stemcomponent 26 of the talar platform 20 is installed. FIG. 31 shows theinstallation of the calcaneal stem component 31 into the passage P.

As FIG. 31 shows, the footholder assembly 102 is pivoted out of itsupright condition to rotate the foot to maximum plantar flexion. Thephysician selects the appropriate angled talar/calcaneal stem 26. Thestem 26 is inserted into the previously formed passage P in the talus 15and calcaneous 17.

A strike block assembly 204 is placed over the proximal end of the stem26. A protective cover (not shown) may be provided for the proximal endof the stem 26, in which case the strike block assembly 204 is placedover the cover. The block assembly 204 is struck to seat the stem 26firmly into the talus 15 and calcaneous 17.

It is desirable that the orientation of the stem 26 and block 204 beessentially parallel to the surface of the talus 15. A wrench 206 orother suitable tool may be used to adjust the orientation if necessary.The stem 26 is struck until the block 204 is flush to the surface of thetalus 15. The stem cover (if used) is then removed.

As FIG. 32 shows, the wrench 206 is placed under the fitting 208 on theproximal end of the stem 26. The physician places the talar artificialjoint surface 24 on the stem 26 in the desired orientation. Bone cementmay be applied to the bottom surface of the talar artificial jointsurface 24 if desired. The surface 24 is set onto the stem 26 bystriking a strike block 210 with a mallet or other suitable tool (notshown). The block 210 then struck until the bottom of the surface 24 isseated flush on the surface of the talus 15. The wrench 2 06 may then beremoved.

7. Insertion of the Tibial Artificial Joint Surface

The physician next determines the optimal tibial artificial jointsurface 22 using sizing blocks (not shown).

As shown in FIG. 33, with the foot placed in plantar flexion, and thesurface 22 is placed into the tibial platform 12, as represented by thearrow. If desired, the surface 22 may be marked for easy placementreference. For example, the face may be marked MED-R (for the right footor MED-L for the left foot) to clearly indicate that the marking shouldbe on the medial side of the surface 22 (not shown).

The foot is then checked for proper articulation. The incisions may thenbe irrigated and closed.

a. A Representative Installation Platform

FIGS. 34 and 35 show a representative main installation platform 212 towhich a variety of jigs, fixtures, reamers, and auxiliary platforms ofthe form, fit, and function just described, may be rigidly and simplyaffixed. These jigs, fixtures, reamers, and auxiliary platforms have theform, fit, and function to accomplish the sequence of tasks, asdescribed, including (i) the alignment of the ankle joint with thetibia, (ii) the establishing of an in-line intramedullary path throughthe calcaneus, talus, and tibia; (iii) the establishing of anterioraccess for the purpose of making properly oriented bony cuts in thetalus and tibia to install the tibial and talar platforms 12 and 20;(iv) the installation of the tibial and talar platforms 12 and 20.Preferably, these jigs, fixtures, reamers, and auxiliary platforms areremovable as desired, to allow unobstructed surgical access to the anklejoint. The main installation platform 212 is desirably designed tofacilitate cleaning and sterilization for re-use, though some parts maybe acceptable for single use only.

The design of the main installation platform 212 is such that a fullrange of leg sizes may be accommodated through a series of adjustments,with final alignment achieved with fluoroscopy, as will be describedlater.

b. Removal of the Prosthesis

The described devices and methods provide for easy replacement of theprosthesis should it be necessary or desirable.

The previously made incision is reopened and the foot is placed inplantar flexion. The talar artificial joint surface 24 is removed byprying from underneath with a flat screwdriver or other suitable tool.In some instances, the joint may need to be distended (e.g., about 3 mm)to remove the surface 24. If necessary, a small hole may be drilled inthe surface 24 and a screw placed into the hole to aid in the removal.The calcaneal stem can then be loosened and removed with pliers.

To remove the tibial component, the bottom foot cannula is reinserted.Remove the tibial tray, and then insert the hex drive through the bottomfoot cannula and sequentially unscrew and remove the stem pieces.

Technical features have been disclosed that include, singly or incombination:

(1) A multi-piece stem component (see, e.g., FIG. 4A) suitable for usein any surgical procedure in which a stem is required for fixation of animplant, whether it is a total joint implant, fusion (arthrodesis)implant, osteotomy fixation implant, or fracture fixation implant. Themulti-piece stem component configuration is ideally suited for securingbone components together in a minimally invasive procedure, in which asmall surgical opening is used to install large components. Two or moresmall stem components can be sequentially attached to one another insitu (see FIG. 4B) to make a larger stem assembly. Representative toolsand methodologies for installing a multi-piece stem component are shownin FIGS. 29A to 29D.

(2) Articulating artificial joint surfaces (see, e.g., FIG. 6)comprising complementary ball-and-socket surfaces that not onlyarticulate, but also allows the artificial joint to rotate about anaxis. This makes possible more uniform wear of the surfaces to maximizefunction and longevity of the prostheses.

(3) Articulating artificial joint surfaces (see, e.g., FIGS. 7A, 7B, and7C) comprising complementary ball-and-socket surfaces that not onlyarticulate and rotate about an axis, but also accommodate fore and aftand lateral translation of the mating joint surfaces relative to thenative bone.

(4) Artificial articulating joint surfaces (see, e.g., FIG. 8A), each ofwhich comprises a saddle-shaped component. The saddle shape isgeometrically characterized as a swept arc, comprising a surface definedby a first arc that is swept along a second arc that is perpendicular tothe first arc. The geometry forms, for each surface, an elongated troughthat curves along an axis.

(5) A prosthesis supporting an artificial joint surface that can beassembled in a snap fit and/or interlocking fashion that providespositive locking means without the use of screws or other fasteners(see, e.g., FIGS. 9, 10, 12A, and 13).

(6) A prosthesis accommodating fitment of a plastic joint surface made,e.g., from ultra high molecular weight polyethylene.

(7) An ankle replacement system that can be installed using minimallyinvasive intramedullary guidance established with respect to the majoraxis of the tibia by minimally invasive access through the calcaneus,through an incision in the bottom of the foot. Intramedullary guidancealong the axis of the tibia makes it possible to make properly orientedbony cuts of the talus and tibia through anterior access to the anklejoint. Proper overall alignment of the total ankle system is achieved indesired alignment and orientation with all the natural axes of thenative ankle joint it replaces, and improved long term results areachieved.

(8) Prostheses, tools, and methodologies that make possible theinstallation of a total ankle system using minimally invasiveintramedullary guidance established with respect to the major axis ofthe tibia.

(9) Prostheses, tools, and methodologies that make possible theinstallation of a total ankle system using minimally invasiveintramedullary guidance established with respect to the major axis ofthe tibia using fluoroscopic visualization.

(10) Prostheses, tools, and methodologies that make possible theinstallation of a total ankle system using minimally invasive anterioraccess to the anile joint for making bony cuts and to install prosthesiscomponents.

(11) Prostheses, tools, and methodologies that make possible theestablishment of an in-line intramedullary path through the calcaneus,talus, and tibia.

Other embodiments and uses of the inventions described herein will beapparent to those skilled in the art from consideration of thespecification and practice of the inventions disclosed. All documentsreferenced herein are specifically and entirely incorporated byreference. The specification should be considered exemplary only withthe true scope and spirit of the invention indicated by the followingclaims. As will be easily understood by those of ordinary skill in theart, variations and modifications of each of the disclosed embodimentscan be easily made within the scope of this invention as defined by thefollowing claims.

What is claimed is:
 1. A prosthesis system, comprising: a firstprosthesis, comprising: a stem having a first end and a second end, thefirst end of the stem including a first engagement feature, the stemhaving a circular cross-sectional geometry sized and configured to bedisposed in an intramedullary path formed in a first bone; a platformhaving a second engagement feature located on a first side of theplatform and a third engagement feature located on a second side of theplatform, the second engagement feature of the platform beingcomplementary to the first engagement feature of the stem for couplingthe stem to the platform, and a first artificial joint surface rotatablycoupled to the platform and including a fourth engagement feature, thefourth engagement feature of the first artificial joint surface beingcomplementary to the third engagement feature of the platform forcoupling the first artificial joint surface to the platform, wherein thecoupling between the first artificial joint surface and the platform issuch that the first artificial joint surface may translate relative tothe platform when the prosthesis system is implanted in a patient; and asecond prosthesis, comprising: a second artificial joint surfaceconfigured to be attached to a second bone and to articulate with thefirst artificial joint surface, wherein the first artificial jointsurface and the second artificial joint surface include mating concaveand convex surfaces, wherein the platform comprises a cylindrical collarextending away from the stem when the platform is fixedly coupled to thestem, and wherein the cylindrical collar is configured to be received ina complementary recess defined by the first artificial joint surface toprovide a rotational fit between the platform and the first artificialjoint surface.
 2. The prosthesis system of claim 1, wherein the firstartificial joint surface comprises a concave dome and the secondartificial joint surface comprises a convex dome configured to mate withthe concave dome.
 3. The prosthesis of claim 1, wherein the firstartificial joint surface is coupled to the platform by a loose,non-interference fit.
 4. The prosthesis of claim 3, wherein the firstartificial joint surface is configured to translate in at least one of alateral direction or an anterior-posterior direction.
 5. An ankleprosthesis system, comprising: a first prosthesis, comprising: a stemhaving a first end and a second end, the stem having a circularcross-sectional geometry sized and configured to be disposed in anintramedullary path formed in an inferior end of a tibia such that, whenimplanted, the stem extends along an axis defined by the tibia, the stemincluding a first engagement feature disposed at the first end; aplatform having a second engagement feature located on a first side ofthe platform and a third engagement feature located on a second side ofthe platform, the second engagement feature of the platform beingcomplementary to the first engagement feature of the stem for couplingthe stem to the platform, and a first artificial joint surface includinga fourth engagement feature, the fourth engagement feature of the firstartificial joint surface being complementary to the third engagementfeature of the platform for coupling the first artificial joint surfaceto the platform such that the first artificial joint surface is able torotate and translate relative to the platform when the ankle prosthesissystem is implanted in a patient; and a second prosthesis, comprising: asecond artificial joint surface configured to be attached to a talus andto articulate with the first artificial joint surface, wherein the firstartificial joint surface and the second artificial joint surface includemating concave and convex surfaces, wherein the third engagement featureincludes a cylindrical collar extending away from the stem when theplatform is fixedly coupled to the stem, and wherein the fourthengagement feature includes a recess that is complementary to thecylindrical collar such that the cylindrical collar may be received inthe recess to provide a rotational fit between the platform and thefirst artificial joint surface.
 6. The ankle prosthesis system of claim5, wherein the second artificial joint surface is a convex dome, andwherein the first artificial joint surface includes a concave surfaceconfigured to mate with the convex dome.
 7. The ankle prosthesis systemof claim 5, wherein the first artificial joint surface is translatableto the platform when the ankle prosthesis system is implanted in apatient.
 8. The ankle prosthesis system of claim 7, wherein the firstartificial joint surface is translatable in both an anterior-posteriordirection and a medial-lateral direction when the ankle prosthesissystem is implanted in a patient.
 9. A prosthesis system, comprising: afirst prosthesis, comprising: a stem having a first end and a secondend, the first end of the stem including a first engagement feature, thestem having a circular cross-sectional geometry sized and configured tobe disposed in an intramedullary path formed in a first bone; a platformhaving a second engagement feature located on a first side of theplatform and a third engagement feature located on a second side of theplatform, the second engagement feature of the platform beingcomplementary to the first engagement feature of the stem for couplingthe stem to the platform, the third engagement feature of the platformincluding a tab having a first diameter, and a first artificial jointsurface rotatably coupled to the platform and including a fourthengagement feature comprising a hole having a second diameter that isgreater than the first diameter such that the tab may be received in thehole for coupling the first artificial joint surface to the platform,wherein the coupling between the first artificial joint surface and theplatform is such that the first artificial joint surface may translaterelative to the platform when the prosthesis system is implanted in apatient; and a second prosthesis, comprising: a second artificial jointsurface configured to be attached to a second bone and to articulatewith the first artificial joint surface, wherein the first artificialjoint surface and the second artificial joint surface include matingconcave and convex surface.
 10. The prosthesis system of claim 9,wherein the first artificial joint surface is configured to translate inboth an anterior-posterior direction and a medial-lateral direction whenthe prosthesis system is implanted in a patient.
 11. The prosthesissystem of claim 9, wherein the first bone is a tibia and the second boneis a talus.